Re: [Lsf-pc] Linux kernel impact on PostgreSQL performance

On Tue, Jan 14, 2014 at 3:39 AM, Claudio Freire <klaussfreire@gmail.com> wrote:
> On Tue, Jan 14, 2014 at 5:08 AM, Hannu Krosing <hannu@2ndquadrant.com> wrote:
>> Again, as said above the linux file system is doing fine. What we
>> want is a few ways to interact with it to let it do even better when
>> working with postgresql by telling it some stuff it otherwise would
>> have to second guess and by sometimes giving it back some cache
>> pages which were copied away for potential modifying but ended
>> up clean in the end.
>
> You don't need new interfaces. Only a slight modification of what
> fadvise DONTNEED does.

Yeah.  DONTREALLYNEEDALLTHATTERRIBLYMUCH.

> This insistence in injecting pages from postgres to kernel is just a
> bad idea. At the very least, it still needs postgres to know too much
> of the filesystem (block layout) to properly work. Ie: pg must be
> required to put entire filesystem-level blocks into the page cache,
> since that's how the page cache works. At the very worst, it may
> introduce serious security and reliability implications, when
> applications can destroy the consistency of the page cache (even if
> full access rights are checked, there's still the possibility this
> inconsistency might be exploitable).

I agree with all that.

-- 
Robert Haas
EnterpriseDB: http://www.enterprisedb.com
The Enterprise PostgreSQL Company